Field of the Invention
The present invention relates to an apparatus and a method of correcting luminance unevenness and color unevenness, which are collectively referred to as shading, of an image displayed by an image projection apparatus or a direct-view display apparatus.
Description of the Related Art
Examples of a method of automatically correcting shading, such as luminance unevenness and color unevenness of an image displayed by an image projection apparatus (hereinafter referred to as a projector) or a direct-view display apparatus (hereinafter referred to as a direct-view display), include following methods.
For example, Japanese Patent Laid-open No. 2011-150349 discloses a method of preventing shading of a display image displayed by a projector or a direct-view display, by using a captured image obtained by capturing the display image through an image capturing apparatus. Japanese Patent Laid-open No. 2005-017715 discloses a method of correcting shading, streaky shading in particular, of a display image displayed by a projector, by using a captured image obtained by capturing the display image through an image capturing apparatus.
However, the methods disclosed in Japanese Patent Laid-open No. 2011-150349 and Japanese Patent Laid-open No. 2005-017715 are not applicable to a case where an obstacle (blocking object) is placed between the display image and the image capturing apparatus that captures the display image and thereby the obstacle is captured in the captured image obtained by the image capturing apparatus. For example, in such a method, a measuring device such as a color illuminometer, which can measure a chromaticity, is disposed in front of a display surface (that is, between the display surface and the image capturing apparatus), and a gamma characteristic is set by using a chromaticity of the display image measured by the measuring device. In this method, however, the measuring device is captured as an object in the captured image. When the measuring device is disposed at a back of a hole formed in a projection surface (screen) as a display surface for the projector, the measuring device is also captured as an object in the captured image.
In the method disclosed in Japanese Patent Laid-open No. 2011-150349, since a band-pass filter is applied to the entire captured image obtained by the image capturing apparatus, use of a filter as the band-pass filter having such an intensity that the obstacle disappears from the captured image spoils information relating to the shading in the captured image. The use of such a filter prevents production of a correction value for sufficiently correcting the shading of the display image from the captured image. On the other hand, use of a filter as the band-pass filter having a low intensity produces a correction value corresponding to the obstacle remaining in the captured image, so that applying this correction value to a corresponding part of the display image results in unnecessary strong shading correction.
In typical projectors, a correction circuit that performs the shading correction is configured to have a resolution much lower than that of a light-modulating element, such as a liquid crystal panel or a digital micromirror device (DMD), which modulates light in the projector. Thus, an interpolation process is performed to match the resolution of the correction circuit to the resolution of the light-modulating element. However, correcting a display image including a high frequency image area through the correction circuit may result in insufficient correction of the high frequency image area, in coloring on a low frequency image area due to an influence of the obstacle, and in an unintended color produced in the interpolation process.
These problems occur also when the method disclosed in Japanese Patent Laid-open No. 2005-017715 is applied to a captured image including a captured obstacle.